In a conventional method of yarn-piecing in a pneumatically-operated ringless spinning machine, e.g. an open-end spinning frame having a plurality of spinning units therealong and a travelling yarn piecing machine or unit, a roller is provided in the yarn piecing unit which is engageable with the package of yarn and is rotatable in both directions to wind and unwind the yarn on and from the package in the yarn piecing-up operation. In the event of a yarn break at any of the spinning stations, the roller is rotated first in its reverse direction for unwinding the yarn from the package to and inserting the free end of the broken whereupon the reversible roller is driven in its forward yarn back into the spinning mechanism of the spinning unit, direction to withdraw the pieced-up and spun yarn, to again wind the same on the package. In this method of yarn-piecing, accuracy in determining the unwound length of such yarn greatly influences the success or not of the yarn piecing and, therefore, the quality of the pieced-up yarn.
In such known methods, determination of the exact length of the yarn being unwound from a cone-shaped package by the reversible roller is particularly difficult because the length varies depending on the location on the package from which the yarn is unwound; namely, the length of yarn which is unwound from the small-end of the cone-shaped package is considerably different from that of yarn which is unreeled from the opposite, large-end of the cone. Even when unwinding yarn from a cylindrical-shaped package, the accuracy in determining the unwound length of the yarn is readily affected by the traversing motion of the yarn across the yarn package during the unwinding from the package, on which the yarn is traversely wound up.
Thus, the known conventional method of yarn-piecing in ringless spinning machines has a drawback or disadvantage in that the length of yarn unwound from its package is inaccurate and, therefore, the rate at which yarn-piecing service is accomplished successfully is affected by the inaccuracy.